In US 2003/0236067 A1 there is described a repeater with digital channelizer. In order to retransmit a communication channel at a specific frequency which remains constant over time, a receiver may receive a signal including a specific frequency of the communication channel. An analog to digital converter generates a digital signal correlated to the received signal that may be passed through a digital filter to filter the digital signal and pass frequency components at or around the frequency of the communication channels specific frequency. A digital to analog converter may generate an analog signal correlated to the filtered digital signal and a transmitter may transmit the analog signal.
Further, in US 2007/0015462 A1 there is described a time division duplex TDD controlled repeater. The TDD repeater comprises a scheduling component that analyzes a scheduling relating to when communications are active in the forward link direction and when communications are active in the reverse link direction, wherein the communications are subject to time division multiplexing. An amplifier amplifies received communications as a function of the schedule. The repeater can comprise a configuration component that configures the amplifier to amplify the received communications in one or more of a forward link direction and a reverse link direction.
FIG. 1 shows a basic principle for the operation of a repeater in a wireless communication network.
As shown in FIG. 1, repeaters are widely used in wireless communication networks in order to re-amplify electromagnetic signals. Repeaters receive, amplify and retransmit signals of a particular channel. The amplified signals can propagate over longer distances or it provides better quality, i.e., better signal to noise and interference ratios than the original signals. Repeaters are also known as layer-1 relay or amplify-and-forward relay.
Further, the amplified signals can either be transmitted on different frequency bands when compared to the frequency bands of the original signals through frequency translating or they can be transmitted on the same frequency band, so-called on-frequency. In the latter case self interference has to be avoided, e.g., by means of separated antennas, self-interference cancellation techniques, or by electronic components such as circulators.
As shown in FIG. 1, repeaters amplify resources with the desired carrier signal towards users on the downlink DL or from users on the uplink UL that need repeater support.
However, conventional repeaters continuously amplify the entire channel bandwidth. Even if resources, e.g., TDMA time slots, FDMA sub-channels, or OFDMA resource blocks are currently not used or if resources do not need repeater support, repeaters amplify them. Thus, energy is wasted whenever the repeater amplifies these resources.
FIG. 2 shows the generation of undesired interference signals generated by a repeater operated in a wireless communication network.
As shown in FIG. 2, repeaters also amplify resources without a desired signal. Undesired signals on these resources are for instance:                Interference from a neighbouring cell, which is amplified by the repeater. This degrades the signal quality within the cell. As shown in FIG. 2 this happens for the solid line in UL and the dashed line in DL.        Carrier signals from users that do not need repeater support are amplified. These amplified signals cause interference to neighbouring cells. As shown in FIG. 2 this happens for the solid line on the downlink DL and for the dashed line on the uplink UL. Further, if the processing delay introduced by an on-frequency repeater exceeds the allowed limit, the amplified signal interferers with the original one. In FIG. 2 this is illustrated by the dotted line for the downlink DL and the uplink UL.        The receiver noise of the repeater is amplified, which causes interference within the cell and towards neighbouring cells.        
Further, in conventional repeaters the transmit power of a repeater is equally distributed across the amplified channel. The power amplifier limits the power spectral density of the amplified signal.
Still further, the radio base station may control the repeater via a dedicated control channel. This control channel could tell the repeaters to turn resources on and off. However, the control channel needs to be standardized and it consumes radio resources. Further, a control channel increases the complexity of the radio base station. Due to the necessity to decode control messages the repeater would require baseband processing capabilities. This increases the repeater complexity, too.